It depends. What are you going to be using the computer for, and what are the prices of those two different computers.
The Core i5 is a faster CPU, but the ATi Radeon HD 5450 is a much slower card than the HD 5650, and the HD 5450 is really only suitable for playing old games on low to medium settings, whereas the HD 5650 can handle quite a few games on low to high settings, depending mainly on the age of the title.
Is the Core i5 a Core i5 750 or Core i5 650/660? Because if it is a 600 series Core i5, you're better off with the Core i3/HD 5650 combo, unless you want to just watch 1080p movies, then either computer is fine, I suggest the cheaper of the two.
If you want to do any kind of gaming, I would suggest going no lower than an HD 5750. 58xx are better, but more expensive. 5770 is really good. Of course, only go with the 5000 series if you want DirectX11 and even then, 5750 should be the lowest you go in that series.
Otherwise, look for the 48xx series. Those run just as good as the 57xx series but they only do DirectX 10.1.
If you're not gaming, then the 55xx series aren't bad for things such as business applications and possible as a way to view videos, especially in a home theater PC (HTPC).